The Laboratory Animal Facility at the Fox Chase Cancer Center (FCCC) provides excellent animal care and use support to research investigators and has enjoyed full accreditation by The Association for the Assessment and Accreditation for Laboratory Animal Care International (AAALAC) since its first application in 1969. Since that time the Institute and Animal Research Programs have grown significantly, but there has been little expansion or growth in the footprint of the animal facility. It is now filled to capacity and overcrowded, and the facility must expand and/or make major changes in caging technology. The great majority of animals used and housed are research mice, many of which are transgenic and immunocompromised and require disease free housing facilities and procedures. In 2005 we began a long range plan to systematically convert standard caging and racks to high density ventilated racks. This step alone will increase our holding capacity by almost 80% within the existing footprint. We have consolidated and reduced breeding mice as much as possible to make more space available for research mice and in February 2006 converted a former rodent breeding wing (3,000 sq. ft.) on the second floor into a barrier research area for transgenic and immunodeficient research mice. We have committed institutional funds for renovation and upgrading air handling to this wing and installation of an autoclave at the entry (to be completed in the late summer of 2008), and have purchased high density ventilated cages and racks to house an additional 1760 cages of research mice in this second floor area. We next turned our attention to the research mouse barrier area on the third floor. We have obtained funds to convert approximately one-half of this area to high density racks and cages, that conversion is going on. Funding is now requested for 13 double sided high density HEPA filtered ventilated racks (each housing 180 mouse cages), 9 single sided HEPA filtered high density ventilated racks (each holding 90 mouse cages), and 8 HEPA filtered change stations for this area so that the increasing use of transgenic research mice at Fox Chase can be accommodated. These high density cages will increase the research mouse inventory in this area by 1750 more cages and will complete the conversion of this third floor area to high density ventilated cages and racks. This will be a major step in our long-range plan to accommodate the growing need by funded research investigators for use of transgenic and immunocompromised mice in their research, and along with other internal modifications is critical to accommodate the expected need at Fox Chase through mid-2012. We have also begun longer-range planning for a new, larger facility as part of the Fox Chase five year plan for growth and expansion. These cages are essential at this time and will be used immediately, and can be used in any new facility in the future as our expansion continues.